1. Field of the Invention
This invention relates to a recording medium to be used preferably for ink jet recording method, particularly to a recording medium excellent in ink receptivity and also excellent in sharpness of the recorded image, and also to a recording method by use thereof.
2. Description of the Related Art
Ink jet recording method performs recording by generating small droplets of ink according to various ink (recording liquid) discharging systems, such as electrostatic attraction system, a system of giving mechanical vibration or displacement to ink by means of a piezoelectric element, a system utilizing a pressure of bubbling caused by heating, permitting the droplets of ink to fly and to attach a part or whole thereof onto a recording medium such as paper. This method is now attracting attention as a recording method which generates less noise and enables high speed printing and multi-color printing.
As the ink for ink jet recording, there have been used those composed mainly of water primarily for the reasons of safety and recording characteristics, and in most cases, a polyhydric alcohol is added for prevention of clogging of nozzles and improvement of discharging stability.
As the recording medium to be used for the ink jet recording method, there have been employed recording media comprising a porous ink receiving layer provided on a conventional paper or a substrate called as the ink jet recording paper.
However, as the ink jet recording is improved in performance such as speed-up or multi-color recording and widely spread, higher and broader characteristics are becoming demanded also for the recording medium.
More specifically, the recording medium for ink jet recording for obtaining recorded images of high resolution and high quality is required to satisfy various basic requirements as follows:
(1) reception of ink onto the recording medium should be as rapid as possible;
(2) even when ink dots may be overlapped with each other, the ink attached later should not flow out into the dot attached earier;
(3) ink droplets should not diffuse on the recording medium to result in larger ink dot diameter than is necessary;
(4) the shape of an ink dot should be approximate to a true circle and its circumference should be smooth;
(5) OD (optical density) of ink dot should be high, without obscurity around the dot; etc.
Further, for obtaining a recorded image quality of high resolution comparable to color photography by the multi-color ink jet recording method, the following performances are additively required in addition to the above requisite performances:
(6) the coloring component of ink should be excellent in color forming property;
(7) since liquid droplets which are the same in number as the number of ink colors may be sometimes attached on the same spot to overlap each other, ink fixing characteristic should be excellent;
(8) the surface should have gloss; and
(9) the degree of whiteness should be high.
Further, while the recorded images obtained by the ink jet recording method have been employed in the past exclusively for surface image observation, recording media suitable for uses other than for surface image observation are becoming demanded with improvement in performances or propagation of the ink jet recording device.
Uses of the recording medium other than for surface image observation may include those in which recorded images are projected onto a screen, etc. by means of an optical instrument such as a slide or an OHP (an overhead projector), etc. and those images are observed, color resolution plates during preparation of a positive plate for color printing, and a CMF (color mosaic filter), etc. to be used for color display such as liquid crystal, etc.
When the recording medium is to be used for surface image observation, the diffused light of the recorded image is observed, while the transmitted light through the recorded images is observed in the recording medium in these uses. Accordingly, light transmissivity, particularly excellent linear transmittance is required in addition to the requisite performances in general of the recording medium for ink jet recording.
However, no recording medium satisfying all of these requisite performances has yet been known.
Most of the recording media for surface image observation of the prior art have employed a system in which a porous ink receiving layer is provided on the surface and the recording agent is fixed by permitting the ink to be received into the porous voids, and hence the surface of the recording medium was lacking in gloss due to the porous structure.
On the other hand, in the case of the surface of an ink receiving layer which is non-porous, a non-volatile component such as polyhydric alcohol, etc. in the ink after practicing recording will remain on the surface of the recording medium for a long time, whereby drying and fixing time of ink is prolonged, thus involving the drawbacks such that clothings may be contaminated by contact with the recorded images or that the recorded images may be damaged.